The foreign ministry said a Royal Gibraltar Police (RGP) patrol boat "went on a collision course" on Friday with a Spanish police boat heading to a beach in La Linea, a Spanish town bordering Gibraltar.

"The RGP patrol boat, which was sailing at a high speed, diverted course just a few yards from the Spanish boat, causing a big wave that unsettled the Spanish police vessel," it said in a statement.

"Its irresponsible and reckless manoeuvre created a significant, clear and sudden risk for the safety of both official boats and their crew."

File image of a police boat patrolling the coast off GibraltarCredit:
Geoff Pugh

Spain's secretary of state for foreign affairs, Ignacio Ybanez, asked Britain's ambassador to ensure Britain takes "appropriate measures so these types of behaviours are not repeated".

The foreign ministry said the incident happened one mile to the east of Gibraltar, which is strategically located on the southernmost tip of the Iberian peninsula at the mouth of the Mediterranean.

The RGP patrol boat made no effort to get in touch with the Spanish police vessel, it added.

The Royal Gibraltar Police denied this account, saying its vessel "maintained a safe distance at all times whilst attempting to make contact with the crew (of the Spanish boat) to establish their intentions".

The encounter between the two ships happened just roughly 150 metres off Catalan Bay on the eastern side of Gibraltar, it added in a statement.

A spokesman for the Foreign Office said incursions by Spanish state vessels into British Gibraltar territorial waters "are an unacceptable violation of British sovereignty".

"We will continue to use a range of proportionate diplomatic and naval responses to incidents," he added.

Spain ceded Gibraltar to Britain in perpetuity in 1713 but has long argued that it should be returned to Spanish sovereignty, and the territory remains a source of diplomatic tensions.

In one particularly belligerent row over the disputed waters around Gibraltar, Spanish authorities upped border checks in 2013, creating hours-long logjams and forcing the European Commission to intervene in the crisis.

Spain proposed sharing sovereignty with Gibraltar after Britain voted to leave the European Union last month, saying this could be a prelude to bringing the British overseas territory back under its control.